[test] clarify rpc_net & p2p_disconnect_ban functional tests
Summary:
Pull request description:
small improvements to clarify logic in the functional tests 1. have test logic in `rpc_net.py` match run order of the test 2. remove `connect_nodes` calls that are redundant with the automatic test setup executed by the test framework Noticed when I was trying to debug a test for #19725. Small changes but imo very helpful, because they initially confused me.
Backport of core#19877
Test Plan:
./test/functional/test_runner.py rpc_net p2p_disconnect_ban
Reviewers: #bitcoin_abc, Fabien, PiRK
Reviewed By: #bitcoin_abc, Fabien, PiRK
Subscribers: Fabien
Differential Revision: https://reviews.bitcoinabc.org/D17529